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Mental Disorders And Evolution: What Would Darwin Say About Schizophrenia?

It's a question that's baffled evolutionary theorists for decades: if survival of the fittest is the rule, how have the genes that contribute to serious, debilitating mental disorders survived?

It's been shown that people who suffer from schizophrenia, autism, anorexia and other disorders are less likely to have children. And yet, the genes that cause these disorders aren't going away. In fact, some of the disorders appear to be becoming more common. Evolutionary theory wouldn't predict that.

Scientists have a few theories that attempt to explain this paradox.

One is that the genetic mutations that cause these disorders occurred relatively recently, so not enough generations have passed to allow the evolutionary process to weed them out.

Another theory is that the genetic mutations that cause a disorder in one person somehow make that person's sibling more likely to have children. In a situation like that, the mutation offers a net benefit to a person's family.

A team of Swedish and British scientists recently tested these theories by comparing the rates at which people suffering from mental illness have kids to those of their siblings. The data came from a medical database of more than 2 million Swedes.

The researchers found that the siblings of people who suffer from schizophrenia, autism and anorexia had on average the same or fewer children than the general public, which would seem to confirm the first theory. But they also found that the siblings of people who suffer from depression or substance abuse had significantly more children than the general public, an outcome more in line with the second theory.

We talked with Dr. Peter McGuffin, a professor at King's College London who worked on the study, which was published in the journal Archives of General Psychiatry. Here are highlights from the interview, edited for length and clarity.

Q: You say at the beginning of your paper that "psychiatric disorders have long puzzled researchers by defying the expectations of natural selection." Why?

A: It's particularly the case with schizophrenia, which in this paper and in many other papers has been shown to be a disorder that drastically reduces your fecundity — the number of kids you have. It's often referred to as reduced fertility but, strictly speaking, people with schizophrenia aren't infertile. It's just that they're less often likely to find a partner and have kids.

Schizophrenia is estimated to have a heritability of around 80 percent. Same is true for autism. So if these disorders are very heavily influenced by genes, but the people who have the disorders are less likely to pass on their genes, why aren't the disorders becoming less common in the population?

Q: What are some of the theories as to why this might be going on?

A: There are other gene disorders that have selection pressures against them, but are maintained in the population. A brilliant example of that is sickle cell disease. If you have sickle cell disease, the chances are if it's untreated it's going to kill you before you reach early adult life. Whereas, if you have the sickle cell trait — which is to say, you have one copy of the gene, not two copies — it protects you against malaria if you happen to live in an area where malaria is rife. So there's a selective disadvantage to having the disease, but there's a selective advantage to having the trait.

Q: Your study looked at not just people who were affected by psychiatric disorders, but also their siblings. Why?

A: The hypothesis would be that the relatives of the people who have the disorder, who don't actually have the disorder themselves, are compensating by having more children. I mean, not deliberately compensating by going out and having more children, but there's just something about their makeup that makes them have more kids.

So that's essentially what we were testing in this paper. We were looking at the fecundity of schizophrenics, which we found to be low, as was the fecundity of people with autism. The question is, do their relatives actually make up for this by having more kids because they're advantaged in some way? And the answer is no in the case of schizophrenia, but yes in the case of depression.

Q: If I'm someone who is the sibling of someone who has a psychiatric disorder, what do I need to know? Do I need to think twice about having biological children?

A: You need to know you'll have an increased risk of getting the disorder yourself compared with the general population. The risk in siblings is increased, but it's not increased so dramatically that it ought to stop you from having kids.

These aren't single-gene disorders. These are complex disorders where being a relative is just a risk factor, not a certainty factor.

Q: So ultimately, if I'm the sibling of someone who has one of these disorders, I should be aware of the risks, but it's not something that would make me say "I'm not going to have children."

A: It shouldn't make you say that. And if you are particularly concerned about it and you have more than one relative affected by it in the family, it might be worth seeking [genetic] counseling from an expert who knows what the risks are. [Copyright 2012 National Public Radio

IMO and those I have been around are not having more kids because they are the sibling of a child who has a psychiatric disorder but because they watch the difficulties associated with that disorder / disease and choose not to chance it being genetic.

in our culture, even the dead can be kept alive (life support). where, in that, does evolution fit in? we have disrupted nature to it's fullest and it's certainly one of our many issues.. at the same time, i don't condone just letting the disabled die as that is not humane, but nature is not always so humane.

IMO and those I have been around are not having more kids because they are the sibling of a child who has a psychiatric disorder but because they watch the difficulties associated with that disorder / disease and choose not to chance it being genetic.

I think the basic problem with this article is a lack of understanding of genetics and the 'natural history' of schizophrenia- how often it occurs, inheritance, etc. There's also immensely bad assumptions about how schizophrenia develops and what effects it has in different cultures. And zero knowledge of the changes in fertility of schizophrenics, even in recent times.

Like some have said, schizophrenia is NOT caused by one gene. Many genes are involved. What people call 'environment' - how a person is treated, where he grows up, what he eats - has very, very little to do with schizophrenia. It has nothing to do with trauma, loss, mistreatment. It is not a 'combination of environment and genes'('multifactoral') as so many older books claim. But it's not what people used to think, and it's not the 'environment' most people think of(child rearing, feeding, stress, blah blah blah). It is set in the brain very, very early in life - well before birth. It is 'developmental' - meaning caused by how the brain develops in the first few months of life. Those errors of development are uncovered - usually during the teen and young adult years, when the brain undergoes its last big 'remodeling' job. Millions of brain cells are slated for death at that point - it's a quiet death and it's intentional and natural. But that pruning of extra cells has to go EXACTLY right. Or...

We are just realizing that all the stuff we used to think was 'junk' in our genes, isn't junk at all. Epigenes and other genetic factors influence genes, and genes must 'activate' and 'deactivate' at key points in the development of the brain. The brain goes through extraordinary growth from conception to birth and it doesn't end there - the brain goes through complete 'revolutions' during rapid growth periods at 1 1/2, 7 or 8, and again in teen and young adulthood. And things can go wrong.

Quoting rfurlongg:

Published: November 16, 2012 by David Schultz

It's a question that's baffled evolutionary theorists for decades: if survival of the fittest is the rule, how have the genes that contribute to serious, debilitating mental disorders survived?

And the same few assumptions have been made over and over and over, by one author after the other- I can only assume, in an effort to write something eye-catching: first of all, that anything at all 'baffling' is going on.

It's been shown that people who suffer from schizophrenia, autism, anorexia and other disorders are less likely to have children. And yet, the genes that cause these disorders aren't going away. In fact, some of the disorders appear to be becoming more common. Evolutionary theory wouldn't predict that.

Look - Hitler made it a point to exterminate every single mentally ill, mentally retarded, homosexual and any people with any disability in all the countries under his command. By a few decades after World War II, there were just as many mentally ill, mentally retarded and homosexuals in those countries.

The causative genes are not all inherited! Many are de novo mutations (unique to that person, occur IN that person). These mutations continue to occur at the same rate, spontaneously. Further, almost NINTEY PERCENT of people who have schizophrenia, know of not even ONE relative or ancestor in their family history, who has the illness.

Scientists have a few theories that attempt to explain this paradox.

One is that the genetic mutations that cause these disorders occurred relatively recently, so not enough generations have passed to allow the evolutionary process to weed them out.

Then explain why 2000 year and older texts, describe schizophrenia. The bulk of evidence points to schizophrenia being a VERY old disease.

Another theory is that the genetic mutations that cause a disorder in one person somehow make that person's sibling more likely to have children. In a situation like that, the mutation offers a net benefit to a person's family.

I doubt it. There's a built in assumption there that having MORE children equals success - I also doubt that.

A team of Swedish and British scientists recently tested these theories by comparing the rates at which people suffering from mental illness have kids to those of their siblings. The data came from a medical database of more than 2 million Swedes.

The researchers found that the siblings of people who suffer from schizophrenia, autism and anorexia had on average the same or fewer children than the general public, which would seem to confirm the first theory. But they also found that the siblings of people who suffer from depression or substance abuse had significantly more children than the general public, an outcome more in line with the second theory.

Only a few problems with this one. One is that quite a few people who have a mentally ill person in their family, have depression. Many severe mental illnesses are misdiagnosed as 'depression' or are missed entirely - and with 50 or 60% of mentally ill having substance abuse problems, there are a lot of undiagnosed mentally ill people who are 'counted', not as mentally ill, but as substance abusers. ...this 'phenomenon' may more be measuring our health care system, than anything else....

And remember, this data is for one culture, during one short period of time. That doesn't explain much. And there is absolutely no guarantee that schz. occured in the same pattern hundreds or thousands of years ago- or was viewed or treated the same way....m Onward....

We talked with Dr. Peter McGuffin, a professor at King's College London who worked on the study, which was published in the journal Archives of General Psychiatry. Here are highlights from the interview, edited for length and clarity.

Q: You say at the beginning of your paper that "psychiatric disorders have long puzzled researchers by defying the expectations of natural selection." Why?

Again, the big flaw here is missing the idea that the genes are MUTATED, not INHERITED - but there are additional problems. One is that relatively FEW of a schizophrenic parent's children, have schizophrenia. THeir lifetime adjusted risk of developing schizophrenia is far higher than the general population's, but it's STILL under fifteen percent!

A: It's particularly the case with schizophrenia, which in this paper and in many other papers has been shown to be a disorder that drastically reduces your fecundity — the number of kids you have. It's often referred to as reduced fertility but, strictly speaking, people with schizophrenia aren't infertile. It's just that they're less often likely to find a partner and have kids.

Keep in mind that the fecundity of this disease changed RADICALLY upwards in the last 40 years or so - when the state hospitals were closed and people started getting community based care. Most researchers who have studied THIS phenomenon have said that better treatments and the change to decentralized community based care have created those changes.

Schizophrenia is estimated to have a heritability of around 80 percent. Same is true for autism. So if these disorders are very heavily influenced by genes, but the people who have the disorders are less likely to pass on their genes, why aren't the disorders becoming less common in the population?

Again, the author is totally missing some crucial facts about the illness. GENES. MUTATIONS. NOT INHERITED. REMEMBER HITLER AND THE HOLOCAUST. KILLED EVERY SINGLE MENTALLY ILL PERSON HE COULD FIND. Next generation - JUST AS MANY PEOPLE WITH MENTAL ILLNESS.

Because the genetics of the disease just do not work like he is suggesting it works!

There's also a fundamental assumption made by ALL these authors that 'survival of the fittest' and 'primitive culture' meant that every severely mentally ill person died or was killed! Or at least most of them!

And make no mistake. Many primitive cultures are QUITE CRUEL to the mentally ill. They may have been driven out of the community (like the 'Omega' wolves in the wolf pack), they may have been blamed for the group's misfortunes and they may have been harmed.

But that doesn't mean every culture was like that throughout history.

In fact, even Neanderthals appear to have nurtured and cared for severely physically disabled people - people who were so badly disabled they would have required constant, intensive care, would have to be provided with food, etc. In some cultures in the past, the mentally ill were viewed as 'God's children', and those who cared for them were considered to be doing 'God's work' and were well respected.

In other words, even in the most primitive cultures of man and his ancestors, there is evidence that in some groups, severely disabled people not only survived, but received extensive and complex care, even when it demanded of the resources of the group.

Also don't assume that there was no treatment for schizophrenics at any point til now. Even sedatives 'close down' and protect nerve cells from damage. People have been drinking Lithium in spring water for thousands of years, and other routines and rituals may have helped to calm psychotic people.

Q: What are some of the theories as to why this might be going on?

A: There are other gene disorders that have selection pressures against them, but are maintained in the population. A brilliant example of that is sickle cell disease. If you have sickle cell disease, the chances are if it's untreated it's going to kill you before you reach early adult life. Whereas, if you have the sickle cell trait — which is to say, you have one copy of the gene, not two copies — it protects you against malaria if you happen to live in an area where malaria is rife. So there's a selective disadvantage to having the disease, but there's a selective advantage to having the trait.

Sure, but again, is clinging to the assumption that schizophrenia is always severely disabling. In fact, today, about 65 per cent have 'mild to moderate' disease.

Further, the author may never have been around schizophrenics - it really is not at all difficult to calm and comfort most of them, most of them thrive on routine, and there is no real evidence that a hunter-gatherer or early agrarian society would have been so dangerous for them or because of them.

And as the saying goes, 'there's someone for everyone' - in fact, of most of the severely mentally ill people I've known - they have quite active love lives, have girlfriends, boyfriends, nearly all were married at some point, nearly all had children, and most of those children were not mentally ill.

There's a general tone to the article that schizophrenia is ALWAYS severe and disabling, and that people always in all cultures through time, would have reviled and avoided them. And I just do not know about that. Fact is, most schizophrenics are very appealing and loveable and hurt no one, and most would not disrupt or annoy a community at all. Many people would be very moved to offer help and to provide comfort and kindness.

And quite a few schizophrenics are (and probably were in the past too), extremely talented and intelligent. Poetry, art, stories and keeping history of a group, are all jobs that most schizophrenics would excell at. Being a shaman or prophet for a group wouldn't be impossible - in fact there are no jobs that some schizophrenics could not be good at, except for periods of time when they are quite ill and not able to work. Yet these authors constantly assume there must always have been, something repulsive and dysfunctional about all schizophrenics ,down through all time.

Having just lost a friend who was a lovely writer and poet, I can completely see that people with schizophrenia weren't necessarily viewed so terribly negatively in all culures, in all times.

Ever since the early Medieval period in history, one lovely little town in Belgium has been famous for its treatment of the mentally ill. No matter how sick a person was, each and every member of the community would offer them food and shelter. It was viewed as a very safe, comforting environment and many mentally ill people went to the little town to seek comfort and peace.

You'd also have to consider the 'mental hygeine movement' of hundreds of years ago. The idea there was that if you put a mentally ill person in a clean, healthy environment they will be healthier and more productive. This movement involved providing peaceful, quiet homes and simple jobs for the mentally ill. While it didn't cure anyone, it certainly gave a great many people a 'safe haven' of routine and peace where they could function with less fear and shame. it doesn't make the disease disappear, but people often feel happier and safer in such places.

Just not really following the picture. I would not assume it was true hundreds or thousands of years ago - it certainly isn't true today!

Q: Your study looked at not just people who were affected by psychiatric disorders, but also their siblings. Why?

A: The hypothesis would be that the relatives of the people who have the disorder, who don't actually have the disorder themselves, are compensating by having more children. I mean, not deliberately compensating by going out and having more children, but there's just something about their makeup that makes them have more kids.

I realize that's what that study showed - but I have my doubts that it's a universal phenomenon across all cultures and times.

So that's essentially what we were testing in this paper. We were looking at the fecundity of schizophrenics, which we found to be low, as was the fecundity of people with autism. The question is, do their relatives actually make up for this by having more kids because they're advantaged in some way? And the answer is no in the case of schizophrenia, but yes in the case of depression.

Q: If I'm someone who is the sibling of someone who has a psychiatric disorder, what do I need to know? Do I need to think twice about having biological children?

A: You need to know you'll have an increased risk of getting the disorder yourself compared with the general population. The risk in siblings is increased, but it's not increased so dramatically that it ought to stop you from having kids.

These aren't single-gene disorders. These are complex disorders where being a relative is just a risk factor, not a certainty factor.

Actually, the occurence of schizophrenia is so LOW in siblings, parents and relatives that it has been a constant source of puzzlement (and led to the idiotic 'mutlifactoral model' - a model which actually means, 'we haven't got a clue'). It just has NEVER behaved like a 'single gene, inherited' disease. And that's largely because, that isn't what it is!

Q: So ultimately, if I'm the sibling of someone who has one of these disorders, I should be aware of the risks, but it's not something that would make me say "I'm not going to have children."

It's a personal choice - some people are going to decide not to have children, some will go ahead. Some who decide NOT to have children will be doing so under the assumption that schizophrenia inherits like a single gene disease, and they may believe their child's risk is 50% or more - it is not. But some people actually understanding the real rates, will STILL decide not to have a child.

The lifetime adjusted risk is far, far higher for people whose parents or siblings are affected with the illness. But it's still under 15%!

How can that be? Because the lifetime adjusted risk for schizophrenia is so LOW to start with - for the general population.

A: It shouldn't make you say that. And if you are particularly concerned about it and you have more than one relative affected by it in the family, it might be worth seeking [genetic] counseling from an expert who knows what the risks are. [Copyright 2012 National Public Radio

THere is one situation where the risk changes and the reproductive advice changes. That is when a family has an unusually high risk (probably STILL not 50% though....)- many family members have schizophrenia, bipolar, autism, severe unipolar depression...it's called 'family loading'.

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